A chemical sensor is a sensor using, as a sensing principle, a density change of conduction electrons on a surface of a semiconductor material, which is caused by a chemical interaction between a chemical species to be sensed and the surface of the semiconductor material disposed on a sensing part, and an electrical resistivity change of the semiconductor material, which is induced by the density change. For example, in case that the semiconductor material disposed on the sensing part is a metal oxide, when a chemical species to be sensed is attached to a surface of the metal oxide, an oxidation-reduction reaction occurs on the surface of the metal oxide to change the electrical resistivity of the metal oxide, so that the chemical species may be sensed through the electrical resistivity change.
Recently, studies on nano chemical sensors using metal oxides having nanostructures, such as a nanowire, a nanotube, and a nanoribbon, as a semiconductor material included in the sensing part of the chemical sensor, are being actively conducted. This is because the nano chemical sensor using the nano structured metal oxide has a high surface area to volume ratio compared to an existing chemical sensor in which a bulk or thin film semiconductor material is included in the sensing part, and thus is expected to have a higher sensitivity. For example, a study on a nano chemical sensor in which a nanostructure, which is prepared by using a photolithography process, is included in the sensing part, has been reported. Also, for example, Korea Patent No. 1027074 entitled “NANOSTRUCTURE GAS SENSORS AND NANOSTRUCTURE GAS SENSOR ARRAY WITH METAL OXIDE LAYER AND METHOD OF PRODUCING THE SAME” discloses a high sensitive nano chemical sensor in which a nanostructured metal oxide is included in a sensing part.
If a high sensitive chemical sensor, which has an excellent sensitivity to detect an infinitesimal gas, is developed, the high sensitive chemical sensor may be applicable to a national defense and a special purpose as well as various industrial fields, thereby playing a role in creating safer communities. Especially, since a reducing gas including various volatile organic compounds (VOC) is considerably harmful to the human body, and has a high risk of explosion, in case that a high sensitive nano chemical sensor is developed and thus, it is possible to preemptively detect an infinitesimal amount of a reducing gas, the high sensitive nano chemical sensor is expected to be very useful. If a kind of reducing gas, for example, CO is inhaled, since the CO forms carboxy-hemoglobin in blood to disturb an oxygen transfer and reduce an gas exchange performance of red blood cells to cause a death, it is required to detect an infinitesimal amount of CO in a ppm level to hundreds ppm level. However, a high sensitive nano chemical sensor, which is sufficiently sensitive to the reducing gas, was not studied or reported before.